The invention relates to a valve drive for an internal combustion engine. The drive has an elongated securing device or anti-rotation bridge which is referred to as a mounting aid. The device or bridge has receptacle spaces, arranged at intervals one behind the other, for valve tappets. A valve tappet, which is embodied as a roller tappet is arranged in each receptacle space and is secured with a tappet roller directed at a cam of a camshaft and in such a way that the valve tappet can be displaced longitudinally in the receptacle space at right angles to the longitudinal axis of the camshaft. The valve tappet is secured against rotation by two parallel planar key faces, which are formed on its outer surface and which bear against corresponding inner surfaces of the mounting aid.
In the United States, pushrod engines are still in widespread use as combustion engines. For any type of these engines there may be mounting aids for the roller tappets, embodied as either switchable tappets or as standard roller tappets. The respective roller tappets are pressed into a mounting aid and that aid is in turn mounted on the cylinder block. The present invention relates to a simple check as to whether the tappets are arranged in the correct position on the combustion engine.
In internal combustion engines it is known to use a plastic bridge to secure a roller tappet against rotation. The tappet is held in the plastic bridge by face-guiding means. Here, at least one planar face section is formed on the outer surface of the circular-cylindrical tappet, and it interacts with a corresponding planar surface section of a receptacle space of the mounting device. The mounting device may be a plastic part. In order to simplify transportation and mounting of the valve drive parts, the tappets are premounted on the mounting device with a pressure against the interfaces which are in mutual contact with one another.
A mounting device, in which the clamping of the tappets which is necessary for mounting is also effective during later operation of the engine when only the anti-rotation function is required, is disclosed in U.S. Pat. No. 5,088,455. That mounting aid or securing device is injection-molded from plastic with an appropriate glass-fiber reinforcement. However, the mounting aid or securing device is configured only for standard roller tappets, i.e. the positioning and the correct rotation of the tappets are of secondary importance.
As the fuel consumption and thus the emissions of pollutants of all engines also have to be reduced in the United States, future engines will be fitted with cylinder deactivation devices. Those respective cylinders which are to be deactivated are provided with switchable roller tappets which are different than normal tappets. In particular, in eight-cylinder engines, these switchable roller tappets are arranged irregularly with respect to the left-hand or right-hand banks of cylinders of a V8 engine in accordance with the ignition sequence.
Publication DE 197 12 610 A1 discloses a mounting device of an internal combustion engine of the type mentioned at the beginning and explains that combustion engines usually have roller valve tappets which engage with cam elevations of a camshaft. As the tappets cannot rotate about their longitudinal axis because the rollers have to remain on the tappets in the same plane as the cam elevations, the tappets are oriented in a suitable way in the cylinder block of the combustion engine with securing devices, and their rotation is prevented.
An object of the invention is to provide a securing device or mounting aid for the valve tappets of an internal combustion engine in which both standard roller tappets and switchable roller tappets can be mounted reliably at the correct points which are respectively assigned to them and the tappets having correct attitudes.
This object is achieved with the invention in that the mounting aid has both receptacle spaces with a first, e.g. relatively small, interval dimension of the two inner surfaces for bearing the keying faces of standard roller tappets and receptacle spaces with a second, e.g. relatively large, interval dimension of the two inner surfaces for bearing the keying faces of switchable roller tappets. The first and second dimensions may be reversed as to which is the larger, or other distinguishing profiling besides respective interval dimensioning may be selected.
A compression spring which surrounds the tappet and which is secured by means of a supporting plate and a Seeger ring may be arranged in the mounting aid in each receptacle space for a switchable roller tappet. The Seeger ring has a tongue which is integrally formed on its inner surface and which engages in a groove, corresponding in shape to the tongue, in the internal housing of the roller tappet.
Here, the Seeger ring may additionally have a tongue which is integrally formed on its outer surface and which engages in a cutout, corresponding to the shape of this tongue, in the mounting aid.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.